1. Field of the Invention
The present disclosure generally relates to a process cartridge used for an image forming apparatus, and more particularly, to a process cartridge having a function of applying a protective agent to a photoconductor.
2. Description of the Background Art
Typically, an image forming apparatus using electrophotography produces an image by sequentially conducting a series of processes such as a charging process, an exposure process, a developing process, and a transfer process to a photoconductor such as an OPC (organic photoconductor). After conducting the transfer process, by-products generated by discharging during the charging process or toner particles remaining on the photoconductor are removed by a cleaning process. Such cleaning process can be conducted by using a cleaning blade, such as a rubber blade, which has a relatively simple and inexpensive structure but which cleans well.
However, such cleaning blade has a short lifetime and itself reduces the useful life of the photoconductor because the cleaning blade is pressed against the photoconductor to remove residual materials remaining on the photoconductor. More specifically, frictional pressure between the cleaning blade and the photoconductor causes abrasion on the rubber blade and a surface layer of a photoconductor.
Further, small-sized toner particles, used for coping with demand for higher quality images, may not be effectively trapped by such a cleaning blade, referred to as “passing of toner” or “toner passing.” Such toner passing is more likely to occur by insufficient dimensional or assembly precision of the cleaning blade or when the cleaning blade vibrates unfavorably due to an external shock or the like. If such toner passing occurs, higher quality images may not be produced.
Accordingly, to enhance the lifetime of the photoconductor and to produce higher quality images over time, frictional pressure on the photoconductor or cleaning blade needs to be reduced, and a cleaning performance of the photoconductor needs to be enhanced, by which degradation of the photoconductor or cleaning blade can be reduced and the aforementioned “toner passing” can be reduced.
In view of such frictional pressure reduction and cleaning performance enhancement, in general, a lubricant is applied to the photoconductor to form a lubricant layer on the photoconductor using the cleaning blade. Such lubricant layer can protect the surface of the photoconductor from an effect of frictional pressure caused by the cleaning blade pressing against the photoconductor, which abrades the photoconductor, or from a discharge energy effect during a charging process, which degrades the photoconductor. Further, the photoconductor having such lubricant layer can enhance lubricating performance of the photoconductor surface, by which an unfavorable vibration of cleaning blade can be reduced, and thereby toner passing amount can be reduced.
In general, a metallic soap such as zinc stearate is used as the lubricant. However, zinc stearate may adhere to a charge roller of an image forming apparatus and cause unfavorable charging condition, which may result in a lower quality image, for example an image having black streaks.
Research indicates that paraffin can be used as a protective agent providing good lubrication and protection. However, paraffin requires more time to coat the surface of photoconductor compared to zinc stearate after application, by which the photoconductor has some areas coated with paraffin and other areas not coated with paraffin. Such uneven coating may occur when an image forming apparatus, newly shipped from a factory, is used for an image forming operation for the first time. In view of such coating condition, a photoconductor coated with paraffin in advance can be prepared when assembling the image forming apparatus.
Accordingly, the state of the lubricant application on the photoconductor, such as application amount, needs to be evaluated. When zinc stearate is used as the lubricant, a lubricant amount of zinc stearate applied to a photoconductor is analyzed using XPS (X-ray photoelectron spectroscopy), in which the amount of zinc element as a percentage of all elements on the surface of photoconductor is measured.
In XPS analysis, elements other than hydrogen element existing in a top and a sub-surface of a sample can be detected. When an OPC (organic photoconductor) coated with zinc stearate is analyzed using XPS, an element amount profile detected by XPS varies depending on a coating amount or coating ratio of zinc stearate. For example, when no zinc stearate is applied to the OPC, the element amount profile shows an element distribution of the OPC itself, whereas when zinc stearate is applied to the OPC, the element amount profile shows a mixture of the element distribution of the OPC and the element distribution of the zinc stearate. If the zinc stearate is applied to the entire surface of the OPC (i.e., OPC is coated with zinc stearate 100%), the element amount profile only shows the element distribution of the zinc stearate, and therefore an upper limit of zinc amount or ratio on the OPC becomes a zinc amount or ratio of the zinc stearate. Accordingly, when zinc stearate, which has a chemical composition of C36H70O4Zn, coats the entire surface of the photoconductor, theoretically the ratio of zinc to all elements should be 2.44%, which is computed from the ratio of elements in zinc stearate (C36H70O4Zn) excluding hydrogen.
However, when a protective agent, such as paraffin, not containing metal component is applied to the OPC, XPS analysis shows only peak values for carbon (C) and oxygen (O), and therefore the amount of protective agent applied to the photoconductor may not be correctly evaluated.
If the amount of protective agent on a photoconductor cannot be correctly evaluated, a photoconductor having an insufficient amount of protective agent may be assembled in a process cartridge or an image forming apparatus, and such photoconductor can cause image quality degradation.
As such, a conventional analysis method may not be suitable for detecting an amount of a protective agent, such as paraffin, not including metal component. In view of such background, a method of correctly evaluating a surface condition of a photoconductor coated with a protective agent not including metal component is desired.